1. Field of the Invention
The invention is directed to a flush catheter and, more particularly, to a flush catheter provided with a flow directing sheath.
2. Background of the Related Art
In order to obtain clear in-vivo images of arterial walls when using, for example, Optical Coherence Tomography (OCT), it is necessary to displace blood from a cylindrical volume around a tip of an imaging probe. To allow surveying of a length of an artery wall, it is desirable that the cylindrical volume be, for example, as long as approximately 40-50 mm or more. The better the blood is cleared from this volume, the better the image obtained of the arterial wall.
For example, in almost all uses of OCT for imaging during cardiac catherizations, an imaging probe disposed within a guide catheter is inserted into an artery such that a direction of blood flow is from a proximal end of the imaging probe toward a distal end of the catheter or probe. It is desirable that a location of the cleared cylindrical volume be somewhat proximal to the distal end of the catheter, to allow the use of a “minirail” delivery system. A “minirail” delivery system utilizes a guide wire and a flexible tip attachable to the imaging probe. The guide wire is used to guide the imaging probe into the desired artery.
Previous and current methods of achieving the desired cleared volume or blood displacement have included the use of cardiac dilation balloons, the injection of saline through a guide catheter, and the injection of saline through a selective flush catheter inserted over the imaging catheter. All three of these methods provide less than ideal solutions.
The balloon method either involves total occlusion of a vessel for the time that the image is desired, or the use of under-inflated balloons which does not completely remove the blood from the field of view. The guide flush method requires a large flow rate of saline that can over hydrate the patient. This method is also very ineffective when side branches are present.
For example, when blood flow is from a proximal to a distal end of the imaging probe, the selective flush catheter method has the inherent limitation that blood from the area proximal to the flush point is entrained into the flush solution at a point where the flush solution exits the catheter. Increasing the flow rate of flush solution tends to entrain more blood, making it difficult to dilute the blood enough to provide a clear imaging area. In addition, it is difficult to configure this type of device for a minirail delivery system.
U.S. Pat. No. 4,878,893 (hereinafter “the 893 patent”) to Albert K. Chin entitled “Angioscope with Flush Solution Deflector Shield,” which is hereby incorporated by reference, provides a partial solution to this problem, and is intended for use with an angioscope catheter. The 893 patent teaches the use of a curved deflector shield 30 bonded to a distal tip of a catheter 10. The deflector shield 30:                . . . causes the flushing solution to momentarily flow against blood flow toward the proximal end of the catheter. The blood flow will then carry the solution back past the distal tip of the angioscope 18, as shown in FIG. 13 [of the 893 patent] to provide the bolus required for clear visualizationas discussed at col. 5, lines 1-6, of the 893 patent. However, the approach of the '893 patent has several deficiencies which prevent its use in an OCT application and which make it difficult to produce.        
For example, the deflector shield must be at a distal end of the catheter, making it difficult to use a minitail type of delivery system. Further, the design does not strongly direct the flushing solution in an axial proximal direction. This results in much of the flushing solution moving out from the catheter in a radial direction. As such, the bolus of flushing solution does not flow very far toward the proximal end of the catheter and will not provide the long volume desirable for surveying a length of the artery wall. Furthermore, radially directed jets of fluid can damage the sensitive endothelial layer of the vessel and could even perforate the vessel.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.